The present invention relates to a dust collecting apparatus having a plurality of filter bags for filtering an airstream and wherein a jet of pressurized air is periodically injected in the reverse direction into the open end of each filter bag to expel the accumulated particles from the outside surface of the bags.
Conventional self-cleaning dust collectors of the described type typically comprise a sheet metal housing which is divided by a transverse panel having a plurality of rows of openings therein, and so that the panel defines a lower air inlet chamber and an upper air outlet chamber. Cylindrical filter elements, such as fabric filter bags, are mounted so as to be in registry with the openings and they depend downwardly into the inlet chamber. In operation, the dust laden air enters the inlet chamber and the entrained particles are deposited on the outside surfaces of the filter bags, and the filtered air flows upwardly through the inside of the bags and is discharged through the upper outlet chamber.
The filter bags are periodically cleaned by means of a pulse jet, wherein a momentary (e.g. 0.1 second) jet of high velocity compressed air is directed downwardly into each bag. More particularly, the rows of bags are pulsed in sequence, and a continuous flow of air is maintained in the filtering direction since only a small number of the bags are pulsed at any given time. Also, it is conventional to mount a Venturi nozzle in the open end of each bag so that the pulsed jet of air induces additional or secondary air into the bag with the jet of air. The resulting volume of air produces a pressure pulse which travels down the length of the bag and serves to dislodge and expel the accumulated particles on the outside surface. The dislodged particles then fall downwardly into a hopper at the bottom of the housing, where they may be removed. A dust collector of this general type is disclosed in U.S. Pat. No. 3,726,066 to Colley et al.
A problem associated with conventional collectors of the above described type is the fact that the accumulated dust particles are expelled from the pulsed bags at a high velocity, and the particles often impact adjacent bags which are not being pulsed, i.e., bags which are in normal operation. Such impacts can result in the penetration of the adjacent bag, which of course reduces its efficiency and life.
The impaction problem also limits the volume of air which can be pulsed into the filter bags, since a high volume would increase the penetration problem to intolerable levels. Thus as a practical matter the volume of air injected during the reverse pulse cleaning operation is limited, and this in turn limits the bag cleaning efficiency since insufficient air may be pulsed to remove a high percentage of the accumulated particles.
It is accordingly a object of the present invention to provide a dust collecting apparatus of the described type and which overcomes the above noted limitations and disadvantages of the prior art.
It is a more particular object of the present invention to provide a dust collecting apparatus which provides for a shielding of the filter bags from the particles expelled from the outside surface of adjacent bags during the cleaning of the adjacent bags.
It is also an object of the present invention to provide a dust collecting apparatus which permits the volume of the pulsed air to be substantially increased as compared to conventional designs, and so as to permit a high degree of cleaning of the bags.
It is still another object of the present invention to provide a method of retrofitting a dust collecting apparatus of conventional design so as to achieve the construction and advantages of the present invention.